1. Field of the Invention
The present invention relates to a piezoelectric actuator for use in positioning units for optical devices, drive elements for vibration prevention, fuel injection devices, and the like.
2. Description of the Related Art
Piezoelectric actuators using piezoelectric elements, wherein a plurality of piezoelectric layers that expand according to an applied voltage, and an internal electrode layer for supplying an applied voltage are alternately formed in a laminated structure, are known.
In a piezoelectric actuator, in order that the piezoelectric element is not affected by external influences such as moisture, impact, and the like, the side surfaces of the piezoelectric element are covered with an external packaging resin and enclosed in a sealed container.
For example, as disclosed in Examined Patent Publication (Kokoku) No. 6-28832, by enclosing an inert gas in a sealed container, deterioration due to oxidation of the internal electrode layer of a piezoelectric element is prevented and the reliability improved. Also, as disclosed in Unexamined Patent Publication (Kokai) No. 2001-102649, by covering the side surfaces of a piezoelectric element with an external packaging resin, the moisture resistance of the piezoelectric element is improved.
However, sufficiently preventing deterioration of the piezoelectric element of a piezoelectric actuator used under severe environmental conditions is difficult with the structures known to the art and, therefore, a piezoelectric actuator which is reliably resistant to detrimental external influences and has excellent durability is still required.